Solar cells may be defined as devices to convert light energy into electrical energy by using a photovoltaic effect of generating electrons when light is incident onto a P-N junction diode. The solar cell may be classified into a silicon solar cell, a compound semiconductor solar cell mainly including a group I-III-VI compound or a group III-V compound, a dye-sensitized solar cell, and an organic solar cell according to materials constituting the junction diode.
The minimum unit of the solar cell is a cell. In general, one cell generates a very small voltage of about 0.5V to about 0.6V. Therefore, a panel-shape structure of connecting a plurality of cells to each other in series on a substrate to generate voltages in a range of several voltages to several hundreds of voltages is referred to as a module, and a structure having several modules installed in a frame is referred to as a solar cell apparatus.
Typically, the solar cell apparatus has a structure of glass/filling material (ethylene vinyl acetate, EVA)/solar cell/filling material (EVA)/surface material (back sheet). In general, the glass includes low-iron tempered glass. The glass must represent high light transmittance and be treated to reduce the surface reflection loss of incident light. The filling material is interposed between the front/rear side of the solar cell and the surface material to protect a fragile solar cell. In general, the filling material includes thermoplastic polymer or thermosetting polymer, such as EVA. The filling material can be prepared by coating polymer on the solar cell and then applying heat and pressure simultaneously. However, when the heating process is performed for the filling material, air bubbles may be generated. In addition, the initial investment cost is increased and the rework for the defective products is difficult. Further, the filling material may be discolored and the moisture-proof property of the filling material may be degraded if the filling material is exposed to ultraviolet ray for a long time.